Method of forming a sprocket

ABSTRACT

A method of forming a highly accurate sprocket or gear using a combination of spin forming and ironing. An edge of a metal blank disk is split and spin formed into a “T” shape using known methods. A profile, such as a toothed profile, is spin formed into the “T” shaped blank edge to form a sprocket or gear having initial rough dimensions. The spin formed sprocket is then ironed in an ironing die to achieve the final desired dimensions.

FIELD OF THE INVENTION

[0001] The invention relates to a method of forming a sprocket, and more particularly, to a method of forming a sprocket by a combination of spin forming and ironing.

BACKGROUND OF THE INVENTION

[0002] Various methods are known for manufacturing gears and sprockets. Among these, there are two types of flow formed sheet metal gears and sprockets: corrugated and solid back. Corrugated gears and sprockets are for relatively low load applications with a minimal amount of flow or spin forming required. The solid back types are for heavier duty applications, requiring a relatively higher amount of spin forming.

[0003] In a spin forming process, the roller brings each small element of the metal to its elongation limit as it contacts it. As the part continues to spin the roller departs each element quickly, and then re-engages it for more and more forming during each rotation. In spin forming processes where the teeth are formed by a roller or a die that rotates around the part, keeping an accurate dimension with tight tolerances for the teeth, diameters, and the relation between the teeth is extremely difficult since each is rotating on a different center.

[0004] In another method of manufacture, ironing dies are used in press forming to bring a part to its exact size. An ironing ring is a hardened and very precise ring having very accurate dimensions. The ironing ring is pressed around the part, forcing it to conform to the shape of the ironing ring. The amount of shape change made by an ironing ring is limited to fractions of a millimeter.

[0005] In general, the capability of flow forming in a press is limited. Each press stroke can form the material by its elongation limit. For low carbon steels the elongation limit is about 50%. This means if a certain amount of flow forming is required the job may have to be accomplished using a plurality of press stations. This limits the amount of flow forming that can be accomplished using a press since there is a size and financial limit to the number of stations in a press.

[0006] Representative of the art is U.S. Pat. No. 6,277,024B1 (2001) to Koestermeier which discloses a flow-forming device having a spinning chuck that is axially displaceable relative to the forming device.

[0007] What is needed is a method of forming a sprocket that uses a combination of spin forming and ironing. The present invention meets this need.

SUMMARY OF THE INVENTION

[0008] The primary aspect of the invention is to provide a method of forming a sprocket that uses a combination of spin forming and ironing.

[0009] Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings.

[0010] The invention comprises a method of forming a highly accurate sprocket or gear using a combination of spin forming and ironing. An edge of a metal blank disk is split and spin formed into a “T” shape using known methods. A profile, such as a toothed profile, is spin formed into the “T” shaped blank edge to form a sprocket or gear having initial rough dimensions. The spin formed sprocket is then ironed in an ironing die to achieve the final desired dimensions.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings, which are incorporated in and form a part of the specification, illustrate preferred embodiments of the present invention, and together with a description, serve to explain the principles of the invention.

[0012]FIG. 1 is a perspective plan view of a sprocket blank.

[0013]FIG. 2 is a perspective plan view of a partially spun hub.

[0014]FIG. 3 is a cross-sectional view of an exemplary mandrel and roller.

[0015]FIG. 4 is a cross-sectional view of an exemplary splitting roller arrangement.

[0016]FIG. 5 depicts a split edge.

[0017]FIG. 6 is a perspective view of a “T” surface.

[0018]FIG. 7 is a perspective view of the rough formed sprocket teeth.

[0019]FIG. 8 is a perspective view of the fully formed and ironed sprocket.

[0020]FIG. 9 is a cross-sectional side view of a two ring ironing die.

[0021]FIG. 10 is a cross-sectional side view of a three ring ironing die.

[0022]FIG. 11 is a side view of an ironing die ring.

[0023]FIG. 12 is a plan view of an ironing die ring.

[0024]FIG. 13 is a perspective view of the forming rollers and mandrels engaged with a sprocket being spin formed.

[0025]FIG. 14 is a perspective view of the forming rollers with the mandrels omitted.

[0026]FIG. 15 is a cross-sectional view of the arrangement depicted in FIG. 14.

[0027]FIG. 16 is a detail of FIG. 14, depicting the forming roller and sprocket toothed surface.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0028] A method of manufacturing a gear or sprocket using a combination of spin forming and ironing. First, a blank is spun formed to a desired shape having initial rough dimensions. The part may comprise a toothed sprocket or gear, for example. Spin forming a part to an initial, rough dimension can be performed relatively quickly. Second, the spun formed part is ironed by pressing the part through an ironing die. Ironing forms the part to a desired final dimensional accuracy which would not otherwise be easily or timely produced by spin forming alone. The terms “part”, “sprocket”, and “gear” are usable interchangeably in this specification or as the context otherwise requires.

[0029]FIG. 1 is a perspective plan view of a sprocket blank. Sprocket blank 100 initially comprises a planar disk. The preformed planar disk facilitates use of the blank in the spinning process. The disk comprises a metallic material, such as aluminum, steel or other material amenable to spin forming. Hole H allows proper placement and alignment of the blank in a spin forming machine on a mandrel, see FIG. 3.

[0030]FIG. 2 is a perspective plan view of a partially spun hub. Hub 101 is shown spun into the blank 100 using methods known in the art which generally comprise use of radially moveable spinning rollers and a spinning mandrel. For example, reference is made to U.S. Pat. No. 5,947,853 (1999) to Hodjat et al. which discloses one such exemplary process for forming a hub.

[0031]FIG. 3 is a cross-sectional view of an exemplary mandrel and roller. Roller F1 moves in a direction D over the surface of blank 100. Metal gathered across blank web 111, see FIG. 8, is formed about mandrel M to form hub 101. Roller F2 can be used to stabilize blank 100 during the process as necessary.

[0032] Splines 106, see FIG. 8, can be formed in the hub during spin forming by use of a mandrel M having an outer surface MS which has a ‘negative’ of the splines to be formed in the hub bore 104.

[0033]FIG. 4 is a cross-sectional view of an exemplary splitting roller arrangement. Surface 102, see FIG. 6, is formed in a blank disk edge using a splitting roller and a forming roller, all by a process known in the art. A splitting roller splits an edge of the blank to roughly form a “Y” shape. For example, reference is made to U.S. Pat. No. 4,109,542 (1978) to Kraft which discloses one such exemplary process. More particularly referring to FIG. 4, blank 100 spins in a mandrel M2. Splitting roller SR spins as well. As it spins, splitting roller SR moves radially inward in direction D2 thereby engaging edge 1000 of blank 100.

[0034]FIG. 5 depicts a split edge. Splitting roller moves further radially inward splitting edge 1000 into a “Y” shape 1020. The split edge 1020 is then further spun into a substantially flat surface 102 having a “T” shape by progressively using forming rollers having suitable shapes known in the art. Surface 102 is connected to hub 101 by a web 111 which extends radially from the hub, see FIG. 6.

[0035]FIG. 6 is a perspective view of a “T” surface. Outer surface 102 has a “T” form in cross-section and is connected to web 111. Hub 101 is shown completed. Hub 101 is used for connecting the sprocket to a shaft (not shown). Some flash 105 may be present about a hub edge upon completion of the spin forming process. Flash 105 can be removed during a machining step if necessary.

[0036]FIG. 7 is a perspective view of the rough formed sprocket teeth. Teeth 103 comprise a profile that is suitable for engaging a toothed belt (not shown) for power transmission. Teeth 103 are spun formed in surface 102 using a roller or rollers that rotate in unison with the rotating part while forming the teeth, see FIG. 13 through FIG. 16. Since the teeth are formed to rough dimensions to this stage of the process, tooth edge 110 is typically inclined to a tooth surface and is not yet normal to a sprocket centerline as is the case in a finished sprocket or gear. This is because the metal spreads axially as the rollers forming the teeth 103 press radially inward on surface 102.

[0037] As previously, noted, at this stage of the process the spun formed sprocket teeth are of a rough dimension, typically being approximately 0.2 mm to 0.5 mm oversize, although these are not offered as limiting dimensions. Spin forming to a rough oversize dimension instead of a finished dimension using the spin forming process reduces the time and cost otherwise required to spin form parts to a high precision. Otherwise, in most cases finishing the sprocket teeth or gear to a finished dimension using the spin forming process takes a relatively significant amount of time. Further, the dimensions cannot be closely controlled to a high accuracy due to ‘spring back’ of the metal and the relative accuracy of the rotating parts. The accuracy of the finished sprocket or gear is also affected by the forming rollers and the blank each spinning around its respective rotational center.

[0038] Once the part is initially formed using the spin forming process, the part then is placed in a hydraulic press having an ironing die, see FIG. 9 and FIG. 10. The ironing die does not cut the metal, rather, it flow forms a small amount, approximately 0.1 mm of metal maximum per ironing ring, from the outer contour of the teeth 103 in an axial direction. The metal flow formed by the rings extends in an axial direction of the part is trimmed in a subsequent machining operation. One to five, or more, ironing rings can be used in an ironing die.

[0039] Use of an ironing die step after spin forming to finish a sprocket or gear allows the spinning process to be completed more quickly, thereby producing a part to an initial rough dimension, which is then finishing in a quick, single ironing stroke through a stack of ironing rings to a highly accurate dimension.

[0040]FIG. 8 is a perspective view of the fully formed and ironed sprocket. The final finishing steps include trimming flash 105 from hub 101. Splines 106 may be broached onto a hub bore 104 surface. Splines 106 may also be spun formed during spin forming of the hub by use of a mandrel having a mandrel spline surface ‘negative’ of a desired finished hub spline surface. As the hub is formed by inward pressure of the forming rollers as taught in the art, the splines are formed by flow of the blank material against a mandrel spline surface.

[0041] Tooth edge 110 is machined to be substantially normal to a sprocket axis of rotation to achieve a finished appearance, or as may otherwise be required.

[0042] Following the ironing step, the part, including the hub 101, splines 106 or teeth 103, or any portion or combination thereof can then be case hardened to a depth of approximately 0.5 mm and a hardness value of approximately 60 Rockwell C. The value of 60 Rockwell C is offered by way of example and not of limitation as it is possible to achieve a wide range of hardness's depending upon the needs of a user. For example, the hardness may be in the range from approximately 20 Rockwell C to approximately 60 Rockwell C.

[0043] The inventive method results in a finished part that is formed quickly and is highly dimensionally accurate having a dimensional tolerance of approximately ±0.01 mm.

[0044]FIG. 9 is a cross-sectional side view of a two ring ironing die. The ironing die comprises two rings 10, 11 which are stacked together. Rings 10, 11 are clamped into a receiving member R using fasteners F. Receiving member R is connected to platen P2. Platen P1 comprises a ram 20 that is moveable in direction M. The rough spun sprocket or gear 100 is placed on end 21 of ram 20 and pressed through a hole in each ironing ring 10, 11 by a movement M of platen P1, see FIG. 12. Each ironing ring forms the roughly dimensioned teeth 103 to a predetermined dimension as previously described. The number of rings in a stack depends upon the amount of forming required to achieve a desired finished dimension. A movement of platen P1 is accomplished by means known in the art, for example, by a hydraulic system (not shown).

[0045] The number of ironing rings to be used in an ironing die stack is dependent upon the difference between the initial rough dimension and the desired final dimension. More particularly, a predetermined amount of tooth material is formed by each ironing ring, approximately 0.1 mm, so rings can be added or removed from the ironing die stack in order to form the desired total amount of material and thereby give a desired finished tooth dimension.

[0046]FIG. 10 is a cross-sectional side view of a three ring ironing die. The form and operation of the three ring ironing die is the same as described for the two ring ironing die with the exception that a third ring 12 is added to the ironing die ring stack. In each case the last ring has an inner dimension that corresponds to a desired sprocket tooth or gear dimension. Of course, a plurality of ironing die rings maybe used as required.

[0047]FIG. 11 is a side view of an ironing die ring. Ring 10 is flat and has a hole 14 through which the part to be ironed is pressed by ram 20. Hole 14 has a diameter D that corresponds to a desired part diameter at this stage of the ironing process. Referring to FIG. 10, one can appreciate that rings 11 and 12 each have progressively smaller diameters than ring 10. In such case ring 12 has a diameter corresponding to a finished dimension.

[0048]FIG. 12 is a plan view of-an ironing die ring. Ring 10 has a tooth profile 13 which corresponds to the desired tooth profile for the sprocket or part at this stage of the ironing process. Sprocket is pressed through hole 14 during the ironing process. Each ironing ring 10, 11, 12 has a hole such as hole 14 through which the sprocket is pressed during ironing.

[0049]FIG. 13 is a perspective view of the forming rollers and mandrels engaged with a sprocket being spin formed. Sprocket having a surface 102, see FIG. 6, is clamped or engaged between mandrels M1 and M2. Mandrels M1 and M2 comprise a portion of a spin forming machine known in the art. For the purposes of FIG. 13, hub 101 and surface 102 have been spun formed as described in FIG. 6.

[0050] Mandrels M1 and M2 clamp blank 100 in the proper relative position between the forming rollers R1 and R2. Mandrels M1 and M2 rotate blank 100 between forming rollers R1 and R2. Rollers R1 and R2 are moveable inwardly toward an axis of rotation of blank 100, thereby engaging surface 102. Rollers R1 and R2 rotate in directions D1 and D2 respectively. Once engaged, rollers R1 and R2 are pressed progressively inwardly against surface 102, thereby spin-forming teeth 103 in surface 102.

[0051]FIG. 14 is a perspective view of the forming rollers with the mandrels omitted. Mandrels M1 and M2 are deleted to better illustrate the blank in relation to the forming rollers R1 and R2. This FIG. 14 depicts a two forming roller arrangement that provides two forming events per complete rotation of the part. Although two forming rollers are shown, one can appreciate that additional forming rollers may be used about the perimeter of the blank. This will result in a like increase in the number of tooth forming events applied to the part per complete rotation, with a commensurate decrease in the time required to form the part to a rough dimension.

[0052]FIG. 15 is a cross-sectional view of FIG. 14. Forming roller R1 and R2 each have a thickness T2. Teeth 103 have a width T1 at the completion of spin forming. Width T2 is greater than width T1 to assure that teeth 103 are properly supported and formed across the full width T1 once final machining takes place as described in FIG. 8.

[0053]FIG. 16 is a detail of FIG. 14, depicting the forming roller and sprocket toothed surface. Rollers R1 and R2 are wider than sprocket 100 being formed in order to fully form a tooth profile across the entire width of the finished sprocket.

[0054] Although a form of the invention has been described herein, it will be obvious to those skilled in the art that variations may be made in the construction and relation of parts without departing from the spirit and scope of the invention described herein. 

I claim:
 1. A method of forming a sprocket comprising the steps of: splitting an edge of a rotating disk; forming a flat surface with the split edge; spinning a profile into the flat surface; and ironing the profile.
 2. The method of claim 1 further comprising the step of: spinning a toothed profile into the flat surface.
 3. The method of claim 1 further comprising the step of: trimming an excess material from the sprocket.
 4. The method of claim 1 further comprising the step of: case hardening the sprocket.
 5. The method of claim 4 further comprising the step of: case hardening the sprocket to a hardness in the range of approximately 20 Rockwell C to 60 Rockwell C.
 6. The method of claim 5 further comprising the step of: case hardening the sprocket to a depth of approximately 0.5 mm.
 7. A method of forming a sprocket comprising the steps of: splitting an edge of a rotating disk; spin forming a hub in the disk; spin forming a bore in the hub; spin forming the split edge into a substantially flat surface; spin forming the substantially flat surface into a profile; and ironing the profile to a finished dimension.
 8. The method as in claim 7 comprising the step of; broaching a bore in the hub.
 9. The method as in claim 7 comprising the step of: trimming an excess material from the hub.
 10. The method as in claim 7 comprising the step of: hardening the hub.
 11. The method as in claim 8 comprising the step of broaching splines on a hub bore surface.
 12. The method as in claim 7 comprising the step of spin forming splines on a hub bore surface.
 13. The method of claim 7 further comprising the step of: case hardening the sprocket to a hardness in the range of approximately 20 Rockwell C to 60 Rockwell C.
 14. The method of claim 7 further comprising the step of: case hardening the sprocket to a depth of approximately 0.5 mm. 